Patent Application
20140304957
The invention relates to a fiber composite material including fibers and a resin connecting the fibers. Additionally, the invention relates to a method for producing a fiber composite material including fibers and a resin connecting the fibers.
Fiber composite materials are multi-phase or mix materials which include a bedding matrix made from resin and reinforcing fibers. Through interaction of the two components a fiber composite material has better properties than the fibers or the resin respectively by themselves. In particular when using extremely thin fibers with a diameter of only a few micro-meters, the so-called effect of specific strength influences the fiber composite material in a positive manner. A reason for this effect is the increasing alignment of the molecule chains of the fibers for a reduced diameter in the decreasing cross-sectional surface that is provided. The plurality of extremely thin fibers also leads to a distribution of the fracture inducing voids in the material to very large distances. A material void in a fiber this way cannot cause a failure of the entire component produced from the fiber but initially only a fracture of an individual fiber in the composite. Therefore fiber composite materials are characterized by excellent properties which are achieved through optimum interaction of both components. In particular fiber composite materials have a very good ratio of strength to weight.
As fibers for fiber composite materials, typically glass fiber, carbon fibers, ceramic fibers (aluminum oxide, silicon dioxide, etc.), aramide fibers, metal fibers, in particular steel fibers and natural fibers (from flax, hemp, jute, sisal, etc.) are being used. The resin matrix of the known fiber composite materials is typically formed by duromeres (synonyms: duroplast, synthetic resin) elastomeres or thermoplasts.
Typical embodiments of fiber composite materials are so-called laminates in which the advantages of an individual fiber orientation are being used. Laminates often include a plurality of fiber mats that are placed on top of one another with different main fiber orientations. For laminate production, typically methods like manual placement, manual placement with vacuum pressing, prepreg technology, vacuum infusion, fiber winding and fiber spraying are being used, wherein the latter strictly speaking is not a laminating method since there are no defined layers, whereas the result however has comparable properties like classic laminates.
Besides laminates, fiber composite materials are often also implemented in the form of injection molded components, injection pressed components and extruded components, wherein the unidirectional orientation of the fibers can be practiced with different degrees of success depending on the method.
Last but not least, so-called “sheet molding compounds” (SMC) are known in which resin mats (with additives like hardeners, optional fillers or additives) and cut glass fibers are pre-fabricated and finished after a maturing time in which the viscosity significantly increases, wherein typically a pressing and curing is performed in heated tools after re-liquefaction.
A frequent disadvantage of fiber composite material is the incomplete embedding of fibers into the resin matrix. This occurs typically when subsequently infusing composite structures made from fibers (woven materials, laid tapes, knitted material, fleeces, etc.) and applies in particular for a processing of the fiber monofilaments into threads when using a twisting or threading of monofilaments. The intermediary cavities between the individual filaments can hardly be completely reached or filled considering the viscosity of the resin so that the strength of the materials obtained remains significantly below the theoretically possible amount. Furthermore, the portion of the resin relative to the mass or the volume of the entire fiber composite material from a cost point of view and from energy and environmental points of view is too high.
It is the object of the invention to provide a fiber composite material and a method for a production thereof which is characterized by high strength and minimum resin use.
The object is achieved by a fiber composite material which includes threads which include a plurality of individual filaments and resin that is crosslinkable through the effect of at least one physical variable and/or at least one chemical material, wherein the resin in a non-crosslinked condition is provided essentially free from solvents and the plurality of individual filaments in the thread is cohesive, wherein the individual filaments in the threads are arranged unidirectionally and wherein the threads thus form a composite material in that they adhere to one another at contact surfaces of their respective outer enveloping surfaces through bridges made from resin.
The fiber composite material according to the invention described supra is a semi-finished product since the resin is provided in non-crosslinked condition in which it only has a minor portion of its final strength or hardness and in this intermediary state of the composite material is only used to keep the composite material formed from threads together in order to make it fit to handle at all. The fiber composite material according to the invention is thus characterized by good deformability and flexibility, so that it still can be formed before crosslinking, this means that it can be brought into its final form before the actual crosslinking, this means hardening of the resin occurs in order to produce a finished product from the semi-finishes product, wherein the finished product can certainly be processed further in additional process steps.
An important component is formed by the monofilament threads used for producing composite materials according to the invention, wherein the monofilament threads include a plurality of individual filaments and resin enveloping the individual filaments. The unidirectionally aligned individual filaments in the threads thus constructed are preferably completely embedded by the resin, wherein no air enclosures shall be in the resin anymore. Though the individual filaments are joined by the resin to form a thread that can be handled as a monofilament, the individual fibers, however, are movable relative to one another with respect to their positions. This is important in particular when adjacent threads of the composite material formed from threads can flatten their cross-sections at their contact locations, thus forming greater contact surfaces than this is the case for threads which include twisted individual filaments. The size of the contact surfaces substantially determines the subsequent strength of the fiber composite material after curing the resin.
Another important characteristic of the material according to the invention is the fact that no additional resin has to be used when forming the composite material. Thus, the process of infusing, submerging, spraying, pouring, etc. of a support structure formed from fibers as required for conventional production methods is omitted. Thus, the resin portion for the fiber composite material according to the invention is very small, since the resin is only used where it adheres to the threads or their individual filaments. In spite of the small amount of resin required which renders the material according to the invention producible very environmentally friendly, light but also cost effective, the resin portion, in case this is desired, can be increased through adding more resin that is independent from the threads, for example, to fill the cavities that typically otherwise remain between the threads. It shall be emphasized that also independently from a filling that is rather untypical for the material according to the invention, good cohesion of the threads is assured, since all contact locations of the threads provide good adhesion for gluing together through the “resin bridges”, since the threads that are being used according to the invention are also completely encased by a resin layer at their outer enveloping surfaces. The threads used according to the invention, which are made from individual filaments and their production are described in detail in the international patent application PCT/EP 2010/056 038 filed on May 4, 2010, which is incorporated herein by reference in its entirety.
The important advantages of the fiber composite material provided through the invention thus are large contact surfaces at the contact points of the threads due to their capability to still deform also after production of the intermediate product “fiber composite material with non-crosslinked resin” while maintaining the sub-composite “thread”, wherein typically the cross-section of the thread is theoretically deformable from a circular flattened shape to a rectangular shape. Instead of the line shaped contact portions for geometrically exactly circular threads and parallel alignment of adjacent threads, rectangular contact strips are formed for the material according to the invention, whose surface is accordingly larger which yields better cohesion, this means higher strength of the finished product in crosslinked condition. When adjacent threads extend at an angle of 90° relative to one another, in particular in a case where they cross over at an angle of approximately 90°, instead of a single contact point for geometrically exact cylindrical threads a square contact surface is provided for rectangular flattened threads. Also in this case, a substantial enlargement of the contact surface and thus an increase of the strength are provided. The possible omission of separately adding resin in addition to the threads used renders the processing, this means the production, of the fiber composite material according to the invention particularly simple and clean.
It is furthermore important for the invention that fiber composite material is provided in non-linked condition in order to retain many degrees of freedom for the subsequent use and to let only the subsequent user decide which particular geometric shape the fiber composite material shall assume. The resin is only crosslinked when the material is brought into the desired shape, for example, through bending, pressing, rolling, winding, stretching, laminating, etc.
In order to increase the cohesion of the composite material that is being used as intermediary product and thus to simplify handling and to reduce the risk of undesired dissolving of the composite before curing of the resin, threads adhering to one another can be pressed against one another, wherein preferably the composite material as such is being pressed. Thus, the applied pressure should be moderate and only serve the purpose to couple the threads to one another at their surfaces through bridges of the non-crosslinked resin. The actual curing process of the resin (and if required, another pressing process) is then typically performed at another location at another point in time after the fiber composite material with the non-cured resin is brought into its final shape through additional processing, in particular forming.
In another embodiment of the invention it is provided that the fiber composite material is a knitted material, a laid material, a fleece or a woven material, preferably with linen binding which includes warp threads and/or filling threads which form a monofilament composite, including a plurality of individual filaments and the non-crosslinked resin, wherein the individual filaments of all recited threads are aligned unidirectionally relative to one another. Based on the large contact surfaces between the threads, a material with excellent strength properties can be provided this way.
It is further provided that the fiber composite material is a sandwich material including at least one layer including a woven material, preferably with linen binding and at least one layer including a fleece, wherein the woven material includes threads, preferably only includes threads which include a plurality of individual filaments and the non-crosslinked resin and the fleece is provided with a non-crosslinked resin, in particular infused therewith or sprayed therewith, and the layers are connected with one another through bridges from resin between adjacent threads of adjacent layers in order to form the fiber composite material.
The object is furthermore achieved through a composite material which includes threads which include a plurality of individual filaments and which include the crosslinked resin which connects the individual filaments with one another, wherein the individual filaments are arranged unidirectional relative to one another, so that the threads form an interconnection, wherein the contact surfaces of the outer enveloping surfaces of the threads are connected with one another through bridges of the crosslinked resin.
The material described supra compared to the other material described supra is also a fiber composite material according to the invention, thus a finished product since the resin is provided in crosslinked condition, this means in cured condition. Thus, the composite material has reached its final hardness and can be handled with considerably less care than the material described supra with the non-crosslinked resin. Through crosslinking the resin, the strength is high and the flexibility compared to the non-crosslinked condition of the resin is significantly reduced. Therefore, subsequent shape changes of the material are only possible within very tight limits. The fiber composite material according to the invention with crosslinked resin is therefore particularly suitable for standard products like plates or profiles with various cross-sections, tubes, etc. which are produced in standardized dimensions and are traded and stocked like standard semi-finished products. Also a use as support woven material or laid support material or other types of textile fabrics or also grids is possible. With respect to the strength and the manufacturing method, the same applies as stated supra regarding the composite material with non-crosslinked resin.
Particularly high strength of the fiber composite material is provided when the cross sections of the threads are oval, ellipsoid or rectangular with rounded corners at least in the portion of their contact surfaces, wherein the contact surfaces in the cross-section are at the flattened sides of the oval or of the ellipse or at the long sides of the rectangle. Through the contact surface enlargement an improvement of the coherence is provided through the glue forces caused by the cured resin.
Also for the crosslinked resin, the composite material according to the invention can be a sandwich material, preferably including at least one layer including a woven material, a laid material, a knitted material, etc. and at least one layer including a fleece, wherein the woven material, the laid material or the knitted material includes threads according to the invention with individual filaments in unidirectional orientation with embedded resin. The provided sandwich material can be formed through pressing into a formed component or a profile, in particular a I-, L-, T-, U-, V-, H- or Y-profile and can be crosslinked during pressing or subsequently, in particular through heat impact.
The solution according to the invention furthermore includes a method for producing a fiber composite material including fibers and a resin crosslinking the fibers comprising the following steps:
a) threads are being used for the fiber composite material which respectively include a monofilament composite including a plurality of individual filaments which are kept together through a resin that is crosslinkable under an impact of at least one physical variable and/or a chemical substance, wherein the individual filaments of a thread are respectively aligned unidirectional;
b) a composite material is formed from the threads in that adjacent threads are connected with one another at contact surfaces of their outer enveloping surfaces through bridges of a resin provided in non-crosslinked condition, wherein the connecting resin previously formed a portion of the threads.
The method according to the invention thus uses particular monofilament threads whose individual filaments are movable relative to one another due to the resin not yet being crosslinked, so that the cross-sectional shape of the threads can still be changed under impact of external forces.
Due to the presence of a sufficient amount of non-crosslinked resin in the monofilament threads, in particular also at their entire outer enveloping surface they can be arranged into a composite fleece (textile fabric=woven material, laid material, knitted material, fleece, etc.) through different connection or coupling types without having to use additional resin for achieving reliable cohesion. The non-crosslinked resin is provided in a condition due to storing capabilities and further processing capabilities in which it essentially does not include any more solvent. However, it has a “residual tackiness” which facilitates coupling resin encased threads through contacting them so that the composite thus formed can be handled, this means can be stored, wound, stacked, packaged, etc. without the resin previously already having to be transformed into the crosslinked condition.
Until the crosslinking of the resin is eventually caused the shape of the fiber composite material produced according to the invention can still be changed, which indicates versatile usability.
In order to increase strength for the provided material, the adjacent threads that are respectively connected with one another through a resin bridge can be pressed into one another in the portion of the contact surface. Imparting pressure thus causes a change of the shape of the thread cross-section in the sense of a flattening and thus an increase of the surfaces that are in contact with one another.
Forming the interconnection from threads with non-crosslinked resin according to the method according to the invention is thus provided independently from the crosslinking of the resin and thus from achieving the final strength of the fiber composite material.
Advantageously, pressing the threads together in the interconnection previously formed and crosslinking in particular under the impact of temperature is at least partially performed simultaneously. Thus the manufacturing method is particularly efficient.
Eventually it is proposed according to the invention, that a tubular hollow profile with circular, oval, elliptical or polygonal cross-section is produced from the threads including the non-crosslinked resin embedding their monofilaments and the hollow profile is subsequently formed through longitudinally progressing contraction in a direction perpendicular to the longitudinal axis of the hollow profile to form a profile with reduced cross-sectional surface, preferably using pressure orthogonal to the longitudinal axis of the hollow profile and wherein the resin is crosslinked during forming or subsequent thereto in particular through heat application.
This way, profiles with various cross-sectional shapes can be produced in a very elegant manner from the hollow elements produced prior thereto, wherein a high quality corner or edge formation can be provided through folding.
The invention is subsequently described in more detail based on plural embodiments of fiber composite materials with reference to figures, wherein:
a and
A thread 1 illustrated in cross-section in
The individual filaments 2, 3 of the threads 1 are all oriented unidirectionally, this means they extend parallel to one another and parallel to a longitudinal axis of the thread 1. This alignment of the individual filaments 2, 3 has to be maintained during windup of the threads 1 after their production, but also during the entire subsequent production process of the linen woven material of the fiber composite material 8 (weaving process). For this reason, it is not possible to use the so-called “overhead pull off” for threads from spools that is otherwise widely used in the production of woven materials. Thus it is important that the individual filaments 2, 3 of the threads 1 are also all still unidirectionally aligned in the linen woven material according to
The woven material of the fiber composite material 8 according to
After the weaving process for the fiber composite material 8, including threads 1 with non-crosslinked resin, the fiber composite material can be pressed together lightly without using high temperatures (in particular not above 100° C.). This only improves the interconnection in the portion of the contact surfaces of intersecting threads 1 in order to be able to maintain the integrity of the woven material in non-crosslinked condition of the resin without having to perform the handling processes with extreme caution. Through the moderate pressure perpendicular to the plane formed by the woven material, the threads are only lightly changed in any cross-sectional shape, this means flattened, so that the contact surfaces 12a in the portion of the intersecting threads 1 are comparatively small, namely the width of a strip shaped contact surface 12a is much smaller than the diameter of the thread 1. In the portion of the contact surface 12a, a bridge 13a is configured from non-crosslinked resin which connects the threads 1 that are crossing over, this means in particular the individual filaments 3 of the respective outer zone 5 provided in the threads 1, with one another.
After the woven material of the fiber composite material 8 was stored and transported in non-crosslinked condition of the resin in wound up form, it can be transformed into its end condition using pressure (e.g., 150 to 300 N/cm2) and temperature (above approximately 140° C.) in that the resin is crosslinked and thus cured.
As can be derived in particular from
In practical applications, the reduced thickness 15b of the tissue is approximately 20 to 70% of the original thickness after the weaving process which almost corresponds to twice the diameter of an individual thread 1. It can be furthermore derived from
The increased contact surface 12b or the increased bridge 13b causes a substantial strength increase of the fiber composite material 8 after the pressing process and crosslinking the resin.
After the pressing process and after resin crosslinking, the woven material can be provided with a carrier material (e.g., paper or foil) with a one-sided silicon coating in order to subsequently cut the formed sandwich material into webs and to use it as an adhesive film which glues on one side or on both sides.
The fiber composite material 18 according to
The layers 16, including woven material and 17 including fleece are respectively arranged on top of one another (stacked), wherein the upper and the lower layer 16 are respectively formed by a woven material in order to increase abrasion resistance of the fiber composite material 18 at its surface. The layers 16 including the woven material as illustrated in
The layer 17 including the fleece includes an aramide fleece with an area weight of approximately 25 g/m2 and 40 g/m2. In order to provide a safe connection with the layers 16 of the woven material in non-crosslinked condition and also subsequently in crosslinked condition of the resin, the layers 17 from the fleece are preferably provided with the same resin which is used for embedding the individual filaments in the threads 1 of the woven material of the layers 16. The resin can be applied through infusing the fleece of the layers 17 in a resin bath or through spraying the fleece with the resin. Thus, it is helpful to place the dry fleece onto the woven material, for example, according to
The aramide fiber elements which are initially loosened from the fleece interconnection in the course of infusing or spraying with resin are used as mechanical connection of the individual filaments of the threads 1 among one another and with the adjacent fleece layers and freely movable.
In particular to increase mechanical strength in several directions, the layers 16 of the woven material are arranged rotated in an alternating manner by 45° with reference to the longitudinal direction, for example, of a group of threads (filling threads).
While the thickness 19 of a single layer 16 of woven material is between 0.35 mm and 1.5 mm, the thickness of a layer 17 made from fleece with approximately 0.15 and 0.25 mm is much smaller than the recited material thickness. The nineteen individual layers of fiber composite material 18 illustrated in
Before applying heat for crosslinking the resin, the fiber composite material 18 is pressed together, for example, with a plate press and thus in a direction of the arrow 22 which yields a reduction of the thickness 23 provided after the pressing and curing process.
A wall thickness 26 of the wound tube is approximately between 0.45 mm and 2.4 mm. Depending on the diameter of the used threads, approximately 2 to 60 thread layers are required for achieving a wall thickness in this range. It is also important in this case that when producing the wound composite contrary to classic procedure when producing fiber composite material, no additional resin is used to close the gaps remaining between the particular threads.
In analogy to the sandwich material according to
After completing the winding process and an optional laminating process performed there between (intermediary layers made from fleece) the semi-finished product configured as a tubular profile 24 can be pulled off from the support mandrel. Since the resin in this instant is not crosslinked, the profile 24 has comparatively large flexibility and deformability, so that its shape can be changed within wide ranges under the impact of internal forces. Thus, for example, a pressure can be imparted upon the profile 24, for example, in the direction of the arrow 27 through a suitable tool, e.g. a plurality of press rollers in order to provide multi-stage shape change, wherein this in turn shall be performed by a suitable tool which is schematically illustrated by a dashed line 29 extending at a 90° angle and is supported opposite to the force acting in the direction of the arrow. Thus, the profile 24 in its intermediary condition can have the shape with an indented cross-section according to the dashed lines 30 in the left half of
After a possibly multi-stage forming process, the L-profile 31 is provided as a result, which is depicted in
As a matter of principle, it can be stated with reference to the fiber composite materials 8, 18, 28 according to the invention and the method for their production that the material properties are significantly influenced by the amount of the pressure which is applied after producing a thread composite, wherein the pressure is still applied using the resin in non-crosslinked condition. With increasing pressure, the flattening of the threads and thus the size of the contact surfaces and also of the resin bridges increases which yields higher strength and density of the material but also reduced elasticity. However, with a comparatively small pressure, materials can also be produced with a higher elasticity in cured resin condition and also with greater porosity, this means with greater surface area, which is important in particular for insulation and absorption properties. Also the specific weight of the fiber composite material according to the invention can be varied through selecting a suitable pressure within a rather large range.
Another aspect of the invention is using a pulp, for example, an aramide pulp in order to be able to obtain a filling or reduction of the cavities of the loops 9 of a woven material with a grid structure according to
Producing a fiber composite material of this type is similar to producing paper, wherein the grid shaped woven material is used as a component that remains in the finished fiber composite material as a solid component later on. The resin provided in the threads of the tissue (c.f.
After removing the woven material from the pulp bath, a slight compression of the composite thus provided and a drying preferably through an air flow dryer can be performed at temperatures below 120° C. in order to prevent crosslinking the resin also in this case. After drying a second press process can occur in which in turn the temperature has to be kept at a low level (30° C. at the most). Subsequently, a woven material made from the same fibers or from other fibers can be applied in order to subsequently cause an application of the fibers forming the pulp through a movement through the pulp bath.
Optionally, a Teflon coated grid can be used as tool when applying the pulp fibers, wherein the grid is removed again after the drying process. The process of producing a fiber composite material of this type can also be performed as a flow process like paper production. In analogy to a forming portion of a paper machine the grid woven material is moved through the pulp bath in order to achieve fiber adhesion. Removing the solvent of the pulp bath from the fiber composite material being created can be performed through vacuum suction boxes. Subsequently, the solvent content can be reduced through pressing between rollers analogous to the pressing portion of a paper machine. Eventually additional drying of the material can be achieved through running the fiber composite material web over steam heated cylinders in order to be able to wind the web material in non-heated condition of the resin onto a roller without gluing. Also this material can be used for producing sandwich arrangements in combination with identical web material in a 45° titled configuration.
This application is a divisional of application Ser. No. 13/373,134 filed on Nov. 4, 2011.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13373134 | Nov 2011 | US |
| Child | 14073435 | US |
